Set higher minimum number of decode surfaces when creating cv::cudacodec::VideoReader

[cudawarped]

cv::cudacodec::VideoReader uses the minimum number of decode surfaces for correct decoding. From the NVIDIA documentation:

This guarantees correct functionality and optimal video memory usage but not necessarily the best performance, which depends on the design of the overall application. The optimal number of decode surfaces (in terms of performance and memory utilization) should be decided by experimentation for each application, but it cannot go below ..

Therefore this pull request allows the user to specify a higher minimum number of decode surfaces when creating cv::cudacodec::VideoReader to increase the decoding performace at the cost of GPU memory, if required.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

force_builders=Custom
buildworker:Custom=linux-4,linux-6
build_image:Custom=ubuntu-cuda:18.04

[alalek]

Thank you for contribution 👍